Applications of RF-ID systems oftentimes require a read distance along a length that is considerably longer than the inherent reading distance of a single transponder. State-of-the-art transponders generally offer horizontal reading patterns of anywhere from 10 cm to 150 cm, depending upon the type of antenna and size. A typical example of an application which would require being able to read along a much greater distance would be when locating water or gas pipes, or buried cables or phone lines which lie underground.
Everyone is hesitant and instructed to exhibit great caution when digging in their own yard, for fear of digging into the ground and hitting a water pipe laid years prior by the water company or an electrical cable laid by the phone company. Blueprint drawings of the locations of these underground objects may be available, but may not always be completely accurate as to the exact location of the objects. A better alternative to locating these objects would be to have transponders located on the objects for remote identification ability. If, however, a standard state-of-the-art transponder is located on a 300 cm pipe underground, and a person is using a hand-held reader trying to locate that pipe, unless that person is holding the hand-held reader within approximately 40-50 cm from the location of the transponder on that 300 cm pipe, the reader will not detect the transponder.
Furthermore, it is not enough to know that the pipe has been identified to lie somewhere underground in the read area. Additional location and orientation information such as where does the pipe begin and end and in what direction does it lie with respect to the area of interest is also necessary. If, for example, a buried antenna not only provides a response along the length of a pipe, but also provides a wide antenna pattern on either side of the pipe, the orientation of the pipe would be difficult to exactly define. For example, large antennas do allow object detection or movement in both horizontal and vertical planes with some freedom, however, larger antennas also pick up an increased level of environmental interference signals or noise and thus reduce the actual reading range.
The objects to be identified do not have to be buried for this extension of the transponder read distance to be beneficial or necessary. There are many RF-ID applications in which a transponder with an extended reading range and a specific radiation pattern could benefit the system greatly. For example, when a transponder is located on any long or large object, similar to the buried pipes, the object will not be identified if the reader is further from the transponder than the maximum read distance of the transponder. In addition, since the transponders radiation pattern is somewhat symmetric around the transponder, a specific radiation pattern directed towards the reader may also be advantageous.